Method and Device for Avoiding Transmission Timing Errors

The present disclosure relates to a technique for absolute time synchronization (ATS), and more specifically, to a technique for avoiding a transmission timing error affecting a timing accuracy.

A wireless factory automation system may have many advantages over a wired factory automation system. For example, the wireless factory automation system may have advantages such as enhanced flexibility, improved safety, greater scalability, and ease of shifting between facilities.

In order to support a conveyor belt manufacturing function by sophisticated motion control of the wired factory automation system in the wireless factory automation system, absolute time synchronization (ATS) techniques may be required so that wireless devices (e.g., mobile robots, sensors, and activators) can perform isochronous/sequential cooperative operations at fixed timings. The term ATS may denote synchronization that ensures wireless devices receive precisely the same timing or clock, regardless of their locations.

To achieve ATS in the wireless factory automation system, addressing timing errors becomes crucial. These errors encompass transmission timing errors as well as reception timing errors. While reception timing errors can be partially mitigated, the variability of transmission timing errors due to inherent hardware impairments among communication nodes makes their elimination unfeasible. Consequently, methods are needed to mitigate the impact of transmission timing errors that occur between communication nodes, such as user equipment (UEs).

The present disclosure are directed to providing a method and an apparatus for achieving ATS in a wireless communication-based factory automation system.

According to a first exemplary embodiment of the present disclosure, a method of a reference user equipment (RUE) may comprise: receiving a first error measurement request message from a first base station; receiving a second error measurement request message from a second base station; receiving a first reference signal from the first base station based on the first error measurement request message; determining a first transmission timing of the first base station based on the first reference signal; receiving a second reference signal from the second base station based on the second error measurement request message; determining a second transmission timing of the second base station based on the second reference signal; calculating a difference between the first transmission timing and the second transmission timing; transmitting a first error measurement response message including information on the difference to the first base station; and transmitting a second error measurement response message including information on the difference to the second base station.

The first error measurement request message may include information on transmission resources for the first reference signal, the second error measurement request message may include information on transmission resources for the second reference signal, and each of the first reference signal and the second reference signal may be one of a demodulation reference signal (DMRS), a channel state information-reference signal (CSI-RS), a positioning reference signal (PRS), or a phase tracking-reference signal (PT-RS).

Each of the first error measurement request message and the second error measurement request message may include a type field and a counterpart base station (BS) field, the type field may indicate that a type of an error measurement message is an error measurement request, the counterpart BS field included in the first error measurement request message may be set to an identifier (ID) of the second base station, which is a counterpart BS for which error measurement is desired, and the counterpart BS field included in the second error measurement request message may be set to an ID of the first base station, which is a counterpart BS for which error measurement is desired.

Each of the first error measurement response message and the second error measurement response message may include a type field, a counterpart BS field, a timing difference field, and a compensation BS field, the type field may indicate that a type of an error measurement message is an error measurement response, the counterpart BS field included in the first error measurement response message may be set to an ID of the second base station, which is a counterpart BS for which error measurement is desired, the counterpart BS field included in the second error measurement response message may be set to an ID of the first base station, which is a counterpart BS for which error measurement is desired, the timing difference field may be set to the difference between the first transmission timing and the second transmission timing, and the compensation BS field may indicate a BS that compensates for the difference between the transmission timings.

The first transmission timing may be determined by further considering a first propagation delay for the first base station and the RUE, and the second transmission timing may be determined by further considering a second propagation delay for the second base station and the RUE.

The RUE may be a common RUE between one or more RUEs registered with the first base station and one or more RUEs registered with the second base station.

According to a second exemplary embodiment of the present disclosure, a method of a first base station may comprise: transmitting a first error measurement request message to a reference user equipment (RUE); transmitting a first reference signal to the RUE based on the first error measurement request message; transmitting an error measurement demand message to a second base station; receiving, from the RUE, a first error measurement response message including information on a difference between a first transmission timing of the first base station and a second transmission timing of the second base station; and compensating for the difference to perform downlink communication.

The method may further comprise: requesting transmission of a base station (BS) registration list to one or more RUEs; receiving one or more BS registration lists from the one or more RUEs; and identifying a common RUE registered in common with the first base station and the second base station based on the one or more BS registration lists.

The method may further comprise: requesting transmission of an RUE registration list to one or more base stations; receiving one or more RUE registration lists from the one or more base stations; and identifying the second base station to which the RUE is registered among the one or more base stations based on the one or more RUE registration lists, wherein the RUE is a common RUE registered in common with the first base station and the second base station, and the error measurement request message is transmitted to the second base station having the common RUE.

The method may further comprise: transmitting information on the difference between the first transmission timing of the first base station and the second transmission timing of the second base station to the second base station.

The first error measurement request message may include a type field and a counterpart BS field, the type field may indicate that a type of an error measurement message is an error measurement request, and the counterpart BS field included in the first error measurement request message may be set to an identifier (ID) of the second base station, which is a counterpart BS for which error measurement is desired.

The error measurement demand message may request the second base station to transmit a second error measurement request message or a second reference signal to the RUE.

The first error measurement response message may include a type field, a counterpart BS field, a timing difference field, and a compensation BS field, the type field may indicate that a type of an error measurement message is an error measurement response, and the counterpart BS field included in the first error measurement response message may be set to an ID of the second base station, which is a counterpart BS for which error measurement is desired, the timing difference field may be set to the difference between the first transmission timing and the second transmission timing, and the compensation BS field may indicate a BS that compensates for the difference between the transmission timings.

The first transmission timing may be determined by further considering a first propagation delay for the first base station and the RUE, and the second transmission timing may be determined by further considering a second propagation delay for the second base station and the RUE.

According to a third exemplary embodiment of the present disclosure, a method of a first base station may comprise: transmitting an error measurement demand message requesting transmission of a second reference signal to a second base station; transmitting an error measurement request message to a reference user equipment (RUE); transmitting a first reference signal to the RUE based on the error measurement request message; receiving, from the RUE, an error measurement response message including information on a difference between a first transmission timing of the first base station and a second transmission timing of the second base station; and compensating for the difference to perform downlink communication.

The error measurement demand message may request simultaneous transmission or sequential transmission of the first reference signal and the second reference signal, the error measurement demand message may include transmission resource information of the second reference signal, and the second reference signal of the second base station may be transmitted to the RUE in transmission resources indicated by the transmission resource information.

The error measurement request message may include transmission resource information of the first reference signal and transmission resource information of the second reference signal.

The first transmission timing may be determined by further considering a first propagation delay for the first base station and the RUE, and the second transmission timing may be determined by further considering a second propagation delay for the second base station and the RUE.

The method may further comprise: requesting transmission of a base station (BS) registration list to one or more RUEs; receiving one or more BS registration lists from the one or more RUEs; and identifying a common RUE registered in common with the first base station and the second base station based on the one or more BS registration lists, wherein the RUE to which the error measurement request message is transmitted is the common RUE.

The method may further comprise: requesting transmission of an RUE registration list to one or more base stations; receiving one or more RUE registration lists from the one or more base stations; and identifying the second base station to which the RUE is registered among the one or more base stations based on the one or more RUE registration lists, wherein the RUE is a common RUE registered in common with the first base station and the second base station, and the error measurement demand message is transmitted to the second base station having the common RUE.

According to the present disclosure, the transmission timing errors of various base stations can be equated, and likewise, the transmission timing errors of various controllers can be equated. This effectively establishes ATS among communication nodes, encompassing base stations, controllers, as well as transmission and reception points (TRPs). Consequently, wireless devices can engage in isochronous/sequential cooperative operations, enabling tasks like ultra-precision applications. This, in turn, enhances the overall performance of the factory automation system.

While the present disclosure is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the present disclosure to the particular forms disclosed, but on the contrary, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

In exemplary embodiments of the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B”. Also, in exemplary embodiments of the present disclosure, “one or more of A and B” may mean “one or more of A or B” or “one or more of combinations of one or more of A and B”.

In exemplary embodiments of the present disclosure, “(re)transmission” may mean “transmission”, “retransmission”, or “transmission and retransmission”, “(re)configuration” may mean “configuration”, “reconfiguration”, or “configuration and reconfiguration”, “(re)connection” may mean “connection”, “reconnection”, or “connection and reconnection”, and “(re)access” may mean “access”, “re-access”, or “access and re-access”.

In the present disclosure, a time may refer to a ‘time point’, and a time point may mean a time. A transmission time may mean a transmission start time or a transmission end time, and a reception time may mean a reception start time or a reception end time.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Hereinafter, exemplary embodiments of the present disclosure will be described in greater detail with reference to the accompanying drawings. In order to facilitate general understanding in describing the present disclosure, the same components in the drawings are denoted with the same reference signs, and repeated description thereof will be omitted.

A communication system to which exemplary embodiments according to the present disclosure are applied will be described. The communication system to which the exemplary embodiments according to the present disclosure are applied is not limited to the contents described below, and the exemplary embodiments according to the present disclosure may be applied to various communication systems. Here, the communication system may be used in the same sense as a communication network.

In exemplary embodiments, “an operation (e.g., transmission operation) is configured” may mean that “configuration information (e.g., information element(s) or parameter(s)) for the operation and/or information indicating to perform the operation is signaled”. “Information element(s) (e.g., parameter(s)) are configured” may mean that “corresponding information element(s) are signaled”. The signaling may be at least one of system information (SI) signaling (e.g., transmission of system information block (SIB) and/or master information block (MIB)), RRC signaling (e.g., transmission of RRC parameters and/or higher layer parameters), MAC control element (CE) signaling, or PHY signaling (e.g., transmission of downlink control information (DCI), uplink control information (UCI), and/or sidelink control information (SCI)).

1 FIG. is a conceptual diagram illustrating a first exemplary embodiment of transmission timing errors.

1 FIG. Referring to, in order to achieve absolute time synchronization (ATS) in a wireless communication-based factory automation system (hereinafter referred to as ‘wireless factory automation system’), timing errors may be problematic. The wireless factory automation system may be interpreted as a wireless communication system or wireless communication network. The timing errors may include transmission timing error(s) and/or reception timing error(s). The transmission timing error may refer to a difference between a transmission time point configured for a transmission signal and an actual transmission time point of the transmission signal. A cause of variability of the actual transmission time point may be regarded as a uncontrollable jitter such as a hardware impairment of a transmitter. The reception timing error may refer to a difference between an accurate reception time point and a reception time point obtained by timing estimation.

1 1 2 2 1 2 1 2 1 2 The transmission timing error may vary due to an inherent hardware impairment of each of communication nodes (e.g., base stations (BSs), transmission and reception points (TRPs), nodes, controllers, wireless devices, user equipments (UEs), or the like). It may be impossible to eliminate a transmission timing error on a single one-to-one link. A UEmanaged and/or controlled by a BSmay exist, and a UEmanaged and/or controlled by a BSmay exist. Each of the UEand UEmay be a wireless device. The BSand BSmay be connected by a wire. Synchronization between the BSand BSmay be ATS.

1 1 1 1 1 1 1 1 BS1,UE1 BS1,UE1,TX BS1,UE1,RX When the BStransmits a signal to the UE, in addition to a propagation delay τ, a transmission timing error eoccurring at the BSand a reception timing error eoccurring at the UEmay exist. The propagation delay may be a radio propagation delay. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. For example, a reception timing error with a length of several samples may occur through design of a very short time resolution (e.g., a sample length in the time domain), and impacts of the reception timing error may be insignificant. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BSand/or UEcannot know the transmission timing error. Also, the BSand/or UEcannot control the transmission timing error.

2 2 2 2 2 2 2 2 BS2,UE2 BS2,UE2,TX BS2,UE2,RX When the BStransmits a signal to UE, the in addition to a radio propagation delay τ, a transmission timing error eoccurring at the BSand a reception timing error eoccurring at the UEmay exist. The receive timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BSand/or UEcannot know the transmission timing error. Also, the BSand/or UEcannot control the transmission timing error.

UEs managed and/or controlled by a BS may be subject to a common transmission timing error for the BS. Times of the UEs controlled according to an absolute time of the BS may not be aligned. The common transmission timing error may not affect operations that the UEs perform isochronously/sequentially at absolute timing(s). Different transmission timing errors for each BS may occur between UEs belonging to different BSs. Isochronous/sequential operations may not be performed at absolute timing(s) due to the transmission timing errors. The isochronous/sequential operations in the present disclosure may refer to ‘isochronous operations’, ‘sequential operations’, or ‘isochronous and sequential operations’. In order to achieve ATS in the wireless factory automation system, methods for reducing impacts of a transmission timing error between UEs belonging to different BSs, methods for reducing a transmission timing error between UEs belonging to multiple TRPs belonging to one BS, and/or the like may be required.

2 FIG. is a block diagram illustrating a first exemplary embodiment of a communication node.

2 FIG. 200 210 220 230 200 240 250 260 200 270 Referring to, a communication nodemay comprise at least one processor, a memory, and a transceiverconnected to the network for performing communications. Also, the communication nodemay further comprise an input interface device, an output interface device, a storage device, and the like. Each component included in the communication nodemay communicate with each other as connected through a bus.

200 270 210 210 220 230 240 250 260 However, each component included in the communication nodemay not be connected to the common busbut may be connected to the processorvia an individual interface or a separate bus. For example, the processormay be connected to at least one of the memory, the transceiver, the input interface device, the output interface deviceand the storage devicevia a dedicated interface.

210 220 260 210 220 260 220 The processormay execute a program stored in at least one of the memoryand the storage device. The processormay refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods in accordance with embodiments of the present disclosure are performed. Each of the memoryand the storage devicemay be constituted by at least one of a volatile storage medium and a non-volatile storage medium. For example, the memorymay comprise at least one of read-only memory (ROM) and random access memory (RAM).

Hereinafter, operation methods of a communication node will be described. Even when a method (e.g., transmission or reception of a signal) performed at a first communication node among communication nodes is described, a corresponding second communication node may perform a method (e.g., reception or transmission of the signal) corresponding to the method performed at the first communication node. That is, when an operation of a base station is described, a terminal (e.g., UE) corresponding to the base station may perform an operation corresponding to the operation of the base station. Conversely, when an operation of a terminal is described, a base station corresponding to the terminal may perform an operation corresponding to the operation of the terminal.

In the present disclosure, an apparatus (or entity) for managing and/or controlling wireless devices (e.g., UEs) may be a BS, cell, primary cell, secondary cell, and/or TRP.

In order to achieve ATS between UEs belonging to different BSs (or different TRPs) in the wireless factory automation system, a reference UE (RUE) may be introduced. The impact of transmission timing errors may be reduced by the RUE. The RUE may be expressed by other names (e.g., first UE, first terminal, reference terminal, reference unit, etc.).

3 FIG. is a conceptual diagram illustrating a first exemplary embodiment of a method for avoiding transmission timing errors.

3 FIG. 1 2 1 1 2 2 1 1 1 2 1 1 1 1 BS1,UE1 BS1,UE1,TX BS1,UE1,RX Referring to, a BSand a BSmay be different BSs. The BSmay manage and/or control one or more UEs (e.g., UE). The BSmay manage and/or control one or more UEs (e.g., UE). When the BStransmits a signal to the UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the BSand a reception timing error eoccurring at the BSmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BSand/or UEcannot know the transmission timing error. Also, the BSand/or UEcannot control the transmission timing error.

2 2 2 2 2 2 2 2 BS2,UE2 BS2,UE2,TX BS2,UE2,RX When the BStransmits a signal to the UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the BSand a reception timing error eoccurring at the UEmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BSand/or UEcannot know the transmission timing error. Also, the BSand/or UEcannot control the transmit timing error.

1 2 1 2 1 2 1 2 1 1 2 2 BS1,RUE BS2,RUE When an RUE is located between the BSand the BS, a transmission timing error occurring at each BS may not be identified, but a difference between transmission timing errors of the BSand BSmay be identified using the RUE. The BSand BScan know the location of the RUE. The location of the RUE may be a location with good radio fading channel qualities for the BSand BS, a location with no change in the radio fading channel qualities, or a location where a change in the radio fading channel qualities is insignificant. The BSand/or RUE may know a propagation delay τfrom the BSto the RUE, and the BSand/or RUE may know a propagation delay τfrom the BSto the RUE.

BS1,RUE,RX BS2,RUE,RX 1 2 1 2 1 2 1 2 The reception timing errors eand efor the BS, BS, and RUE may be almost the same when the radio link quality of each of the BSand BSis above a predefined criterion. In the present disclosure, the BSand BSmay be assumed to be connected by wire, and synchronization between the BSand BSmay be assumed to be absolute synchronization.

1 2 1 2 1 2 BS1,RUE BS2,RUE BS1,RUE BS2,RUE BS1,RUE BS2,RUE The BSand BSmay transmit signals for absolute synchronization simultaneously or at a predefined time (e.g., sample time point). The signal for absolute synchronization may be referred to as an absolute synchronization signal. The absolute synchronization signal may be transmitted periodically or aperiodically. The RUE may measure a difference between an arrival time Tof the signal (e.g., absolute synchronization signal) transmitted from the BSand an arrival time Tof the signal (e.g., absolute synchronization signal) transmitted from the BS. In other words, the RUE may measure T−T. Tmay mean a time at which the absolute synchronization signal transmitted by the BSarrives at the RUE. Tmay mean a time at which the absolute synchronization signal transmitted by the BSarrives at the RUE.

BS1,RUE BS2,RUE When the difference τ−Tbetween propagation delays in Equation 1 is denoted as A, the RUE may measure or estimate a difference B between the transmission timing errors based on the difference between arrival times and A. B may be defined as in Equation 2 below.

1 2 1 2 1 2 1 2 1 2 1 2 1 2 The RUE may transmit (e.g., signal) B or information related to B to the BSand/or the BS. The BSand/or BSmay receive B or information related to B from the RUE. The BSand/or BSmay transmit B or information related to B to a control station (e.g., controller) that manages and/or controls the BSs. The control station may receive B or information related to B from the BSand/or BS. The control station may adjust transmission times (e.g., sample time points) of the BSand/or BSusing B or information related to B. Alternatively, the RUE may transmit (e.g., signal) information on the transmission times (e.g., sample time points) of the BSand/or BSto the BSand/or BSwithout a control station.

BS1,UE1,TX BS2,UE2,TX BS1,UE1,TX BS2,UE2,TX BS1,UE1,TX BS1,RUE,TX BS2,UE2,TX BS2,RUE,TX 1 2 1 2 According to the above-described operation, although the transmission timing errors eand efor the UEand UEbelonging to different BSs may not be eliminated, the transmission timing errors eand emay be adjusted to be equal. In other words, if it is assumed that the transmission timing errors of the BSand BSdo not change during a predefined time (e.g., e≈e, e≈e), the difference B between the transmission timing errors in Equation 2 may be obtained. The difference B in the transmission timing errors may be obtained using the RUE.

2 1 2 The BSmay adjust the transmission timing by adding the difference B between the transmission timing errors to the existing transmission time. According to the above-described operation, the UEand UEmay achieve ATS without impacts of the transmission timing errors. Accordingly, sophisticated cooperative operations may be performed.

1 2 When the control station or the RUE transmits information requesting adjustment of the transmission timing for each BS, the information may include the difference B between transmission timing errors and/or an indication of a scheme for adjusting the transmission timing errors to be equal. The scheme of adjusting the transmission timing errors to be equal may be a scheme of advancing the transmission timing of the BSby B/2 and/or a scheme of delaying the transmission timing of the BSby B/2.

4 FIG. is a sequence chart illustrating a second exemplary embodiment of a method for avoiding transmission timing errors.

4 FIG. 1 2 1 2 1 2 1 2 1 2 Referring to, an RUE may be registered with a BSand/or BS, and the RUE may know information on a propagation delay for the BSand/or information on a propagation delay for the BSin advance. The locations of the RUE, BS, and BSmay be fixed, a distance between the RUE and the BSand a distance between the RUE and the BSmay be identified based on the locations of the RUE, BS, and BS, and the propagation delays may be identified based on the identified distances and a propagation speed in a free space (e.g., the speed c of light).

1 401 1 403 2 402 2 404 The BSmay transmit an error measurement request message to the RUE (S). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). The BSmay transmit an error measurement request message to the RUE (S). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). The error measurement request message may include reference signal information (e.g., resource information, transmission resource information). The reference signal may be a demodulation reference signal (DMRS), channel state information-reference signal (CSI-RS), positioning reference signal (PRS), and/or phase tracking-reference signal (PT-RS). The BS(s) may simultaneously transmit the reference signal(s) to the RUE. Alternatively, the BS(s) may sequentially transmit the reference signal(s) to the RUE.

1 2 1 2 1 2 1 2 405 1 406 2 407 1 2 The RUE may receive the error measurement request message(s) from the BSand/or BS. When the error measurement request message is received, the RUE may determine that error measurement is requested. The RUE may receive the reference signals based on the error measurement request messages (e.g., resources indicated by the error measurement request message) from the BSand BS, and may estimate timings based on the received reference signals. After estimating the timings for the BSand BS, the RUE may calculate a difference between a transmission timing error of the BSand a transmission timing error of the BSbased on Equations 1 and 2 (S). The RUE may transmit an error measurement response message including the difference (e.g., difference value) between the transmission timing errors to the BS(S). The RUE may transmit an error measurement response message including the difference between the transmission timing errors to the BS(S). The difference between the transmission timing errors may mean a difference between the transmission timing of the BSand the transmission timing of the BS.

1 2 The BSand BSmay receive the error measurement response message from the RUE, and may improve accuracy of absolute synchronization based on the difference between the transmission timing errors included in the error measurement response message. For example, when UEs belonging to the BSs perform cooperative operations, each of the BSs may transmit a signal earlier or later by the difference between the transmission timing errors in order to improve accuracy of absolute synchronization. Each of the error measurement request message and the error measurement response message may be transmitted based on at least one of SI signaling, RRC signaling, MAC CE signaling, or PHY signaling.

5 FIG. is a block diagram illustrating a first exemplary embodiment of a format 1 of the error measurement request message.

5 FIG. Referring to, the error measurement request message may include an error measurement message type field and an error measurement counterpart BS identifier (ID) field. The error measurement message type field may be referred to as a ‘type field’, and the error measurement counterpart BS ID field may be referred to as a ‘counterpart BS field’. The type field may indicate the type of the message. The type field set to a first value (e.g., 0) may indicate an error measurement request message. In this case, the type of the error measurement request message may be an error measurement request. The type field set to a second value (e.g., 1) may indicate an error measurement response message. In this case, the type of the error measurement message may be an error measurement response. The type field set to a third value (e.g., 2) may indicate a guide message (e.g., error measurement guide message). In this case, the type of the error measurement message may be an error measurement guide.

4 FIG. 1 2 2 1 The counterpart BS field may indicate an ID of a counterpart BS for which error measurement is desired. The counterpart BS field may be configured with information (e.g., physical cell ID (PCI), MAC address) capable of identifying the BS. For example, in the exemplary embodiment of, the counterpart BS field included in the error measurement request message transmitted by the BSmay be set to the ID of BS, and the counterpart BS field included in the error measurement request message transmitted by the BSmay be set to the ID of BS.

6 FIG. is a block diagram illustrating a first exemplary embodiment of a format 1 of the error measurement response message.

6 FIG. Referring to, the error measurement response message may include an error measurement message type field, an error measurement counterpart BS ID field, a transmission timing error difference field, and an error compensation BS selection field. The error measurement message type field may be referred to as a ‘type field’, the error measurement counterpart BS ID field may be referred to as a ‘counter BS field’, the transmission timing error difference field may be referred to as a ‘timing difference field’, and the error compensation BS selection field may be referred to as a ‘compensation BS field’.

The type field may indicate that the type of the message is an error measurement response message. The counterpart BS field of the error measurement response message may be configured identically to the counterpart BS field of the error measurement request message. The timing difference field may indicate a difference between transmission timing errors with the counterpart BS. For example, the timing difference field may indicate a difference between transmission timing errors measured by the RUE based on the reference signals received from the BSs. The timing difference field may include information indicating whether the transmission timing of the BS is earlier or slower, and the information may indicate a sign (e.g., + or −).

1 2 The compensation BS field may indicate a BS to compensate for the difference between the transmission timing errors. When the difference between the transmission timing errors is received, the BS indicated by the compensation BS field among the BSand BSmay compensate for the difference between the transmission timing errors. When the BS that compensates for the difference between the transmission timing errors is negotiated in advance, the BS(s) may ignore the compensation BS field. The compensation BS field set to a first value (e.g., 0) may indicate that the counterpart BS compensates for the difference between the transmission timing errors. The compensation BS field set to a second value (e.g., 1) may indicate that the BS that transmitted the error measurement request message compensates for the difference between the transmission timing errors. The compensation BS field set to a third value (e.g., 2) may indicate that a pre-negotiated BS compensates for the difference between the transmission timing errors. Alternatively, the compensation BS field set to the third value (e.g., 2) may mean ‘don't care’.

7 FIG. is a block diagram illustrating a first exemplary embodiment of a format 2 of the error measurement request message.

7 FIG. 7 FIG. Referring to, the error measurement request message may include an error measurement message type field, a plurality of error measurement counterpart BS ID fields, and a message response request time field. The error measurement message type field may be referred to as a ‘type field’, the error measurement counterpart BS ID field may be referred to as a ‘counterpart BS field’, and the message response request time field may be referred to as a ‘request time field’. Alternatively, the request time field may not be included in the error measurement request message. When a BS requests differences between transmission timing errors for a plurality of BSs, the error measurement request message shown inmay be used. If there are a plurality of counterpart BSs for error measurement, as many counterpart BS fields as the number of the plurality of counterpart BSs may be required. The request time field may indicate a time (e.g., end time) at which a reception operation of the error measurement response message is performed.

8 FIG. is a block diagram illustrating a first exemplary embodiment of a format 2 of the error measurement response message.

8 FIG. 7 FIG. 8 FIG. Referring to, when the error measurement request message shown inis received, the RUE may transmit an error measurement response message shown in. When the error measurement request message indicates a plurality of counterpart BSs for error measurement, the error measurement response message may include a difference of a transmission timing error of each of the plurality of counterpart BSs. If it is difficult to transmit the differences between the transmission timing errors for all of the counterpart BSs until a time indicated by the request time field, the error measurement response message may include the respective differences between transmission timing errors of as many counterpart BSs as transmission thereof is possible. Alternatively, if it is difficult to transmit the differences between the transmission timing errors for all of the counterpart BSs until the time indicated by the request time field, an additional time for transmission of the differences between the transmission timing errors may be requested.

7 FIG. 8 FIG. 7 FIG. 8 FIG. When the error measurement request message shown inand the error measurement response message shown inare used, the number of exchanges of messages for error measurement may decrease. Accordingly, radio resources may be efficiently used. When a cooperative operation with the BSs is required, the error measurement request message shown inand the error measurement response message shown inmay be used.

4 FIG. 9 FIG. 1 2 1 2 1 2 1 2 In the exemplary embodiment of, each of the BSand BSmay transmit the error measurement request message to the RUE without a request from the RUE. For cooperation, the BSand BSmay simultaneously or sequentially transmit the error measurement request messages to the RUE. When the error measurement request messages are sequentially transmitted, an interval between transmission of the error measurement request message of the BSand transmission of the error measurement request message of the BSmay be short. Only one of the BSs may transmit the error measurement request message. In an exemplary embodiment ofbelow, one of the BSand BSmay transmit the error measurement request message.

9 FIG. is a sequence chart illustrating a third exemplary embodiment of a method for avoiding transmission timing errors.

9 FIG. 1 901 1 902 1 1 Referring to, a BSmay transmit an error measurement request message to an RUE (S). The error measurement request message may include reference signal information (e.g., resource information, transmission resource information). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). The RUE may receive the error measurement request message from the BS. When the error measurement request message is received, the RUE may determine that error measurement is requested. The RUE may receive the reference signal based on the error measurement request message (e.g., resources indicated by the error measurement request message) from the BSand may estimate a timing based on the received reference signal.

2 1 2 903 2 904 2 905 2 905 2 If the error measurement request message is not received from a counterpart BS (e.g., BS) within a preconfigured time from a reception time of the error measurement request message of the BS, the RUE may request the BSto transmit an error measurement request message or a reference signal (S). When transmission of an error measurement request message is requested from the RUE, the BSmay transmit an error measurement request message to the RUE (S). The error measurement request message may include reference signal information (e.g., resource information, transmission resource information). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). When transmission of a reference signal is requested from the RUE, the BSmay transmit a reference signal for error measurement to the RUE (S). In other words, when transmission of a reference signal is requested from the RUE, transmission of the error measurement request message of the BSmay be omitted.

2 904 905 905 2 904 905 2 905 2 904 As another method, when transmission of the error measurement request message or transmission of the reference signal is requested from the RUE, the BSmay perform the steps Sand Sor may perform only the step Sas needed. If it is required to receive information on a difference between transmission timing errors, the BSmay perform the steps Sand S. If it is not required to receive information on a difference between transmission timing errors, the BSmay perform only the step S. In other words, if it is not required to receive information on a difference between transmission timing errors, the BSmay not perform the step S. The RUE may transmit information on a difference between transmission timing errors only to the BS that has transmitted the error measurement request message.

2 1 2 1 2 906 1 907 2 2 908 The RUE may receive the reference signal from the BSand may estimate a timing based on the received reference signal. After estimating the timings for the BSand BS, the RUE may calculate a difference between the transmission timing error of the BSand the transmission timing error of the BSbased on Equations 1 and 2 (S). The RUE may transmit an error measurement response message including the difference (e.g., difference value) between the transmission timing errors to the BS(S). When the error measurement request message of the BSis received, the RUE may transmit an error measurement response message including the difference between the transmission timing errors to the BS(S).

2 2 2 1 2 1 1 When the error measurement request message of the BSis not received (e.g., when only the reference signal of the BSis received), the RUE may not transmit the error measurement response message including the difference between the transmission timing errors to the BS. In this case, the BSmay receive the error measurement response message from the RUE, and the BSmay not receive the error measurement response message from RUE. When the error measurement response message is transmitted only to the BS, the error compensation BS selection field included in the error measurement response message may indicate that the BScompensates for the difference between the transmission timing errors.

1 2 9 FIG. The BSand/or BSmay receive the error measurement response message from the RUE, and may improve accuracy of absolute synchronization based on the difference between the transmission timing errors included in the error measurement response message. For example, when UEs belonging to the BSs perform cooperative operations, each of the BSs may transmit a signal earlier or later by the difference between the transmission timing errors in order to improve accuracy of absolute synchronization. In the exemplary embodiment of, a format 3 of the error measurement request message may be used.

10 FIG. is a block diagram illustrating a first exemplary embodiment of a format 3 of the error measurement request message.

10 FIG. Referring to, the error measurement request message may include an error measurement message type field, an error measurement counterpart BS ID field, an error measurement request field for a counterpart BS, and an error compensation BS request field. The error measurement message type field may be referred to as a ‘type field’, the error measurement counterpart BS ID field may be referred to as a ‘counterpart BS field’, the error measurement request field for the counterpart BS may be referred to as a ‘measurement request field’, and the error compensation BS request field may be referred to as a ‘BS request field’.

The measurement request field set to a first value (e.g., 0) may indicate that transmission of an error measurement request message or reference signal is not requested to the counterpart BS. The measurement request field set to a second value (e.g., 1) may indicate that transmission of an error measurement request message is requested to the counterpart BS. The measurement request field set to a third value (e.g., 2) may indicate that transmission of a reference signal is requested to the counterpart BS.

1 2 2 1 2 2 The RUE may receive the error measurement request message from the BSand request the BSto transmit an error measurement request message or reference signal based on a value of the measurement request field included in the error measurement request message. Alternatively, the RUE may not make any request to the BSbased on the value of the measurement request field included in the error measurement request message of the BS. In this case, the RUE may wait to receive an error measurement request message or reference signal from the BSwithout a request to the BS.

2 1 The BS request field may indicate a BS (e.g., primary BS) that compensates for an error (e.g., difference between transmission timing errors). The BS request field set to a first value (e.g., 0) may indicate that the counterpart BS (e.g., BS) compensates for a difference between transmission timing errors. The BS request field set to a second value (e.g., 1) may indicate that the BScompensates for a difference between transmission timing errors. The RUE may identify the value of the BS request field of the error measurement request message(s) received from the BS(s), and set the value of the error compensation BS selection field of the error measurement response message based on the identified value.

9 FIG. 11 FIG. 2 2 In the exemplary embodiment of, the RUE may request the BSto transmit an error measurement request message or reference signal for error measurement. For the above-described operation, the RUE may use radio resources. In an exemplary embodiment ofbelow, the operation in which the RUE requests the BSto transmit an error measurement request message or reference signal for error measurement may be omitted, and waste of radio resources may be prevented.

11 FIG. is a sequence chart illustrating a fourth exemplary embodiment of a method for avoiding transmission timing errors.

11 FIG. 1 1101 1 1102 1 1 Referring to, a BSmay transmit an error measurement request message to an RUE (S). The error measurement request message may include reference signa information (e.g., resource information, transmission resource information). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). The RUE may receive the error measurement request message from the BS. When the error measurement request message is received, the RUE may determine that error measurement is requested. The RUE may receive the reference signal based on the error measurement request message (e.g., resources indicated by the error measurement request message) from the BS, and may estimate a timing based on the received reference signal.

1 2 1 2 1103 1 2 The BSand BSmay be connected by wire. The BSmay transmit an error measurement demand message to the BS(S). The error measurement demand message may request transmission of at least one of an error measurement request message and a reference signal to the RUE. The BSmay immediately transmit the error measurement demand message to the BS, and accordingly, a time for the RUE to measure a difference between transmission timing errors may be reduced.

2 1 1 2 1104 2 1105 1 2 1105 1 2 The BSmay receive the error measurement demand message from the BS. When transmission of an error measurement request message is requested from the BS, the BSmay transmit an error measurement request message to the RUE (S). The error measurement request message may include reference signal information (e.g., resource information, transmission resource information). After transmitting the error measurement request message, the BSmay transmit a reference signal for error measurement to the RUE (S). When transmission of a reference signal is requested from the BS, the BSmay transmit a reference signal for error measurement to the RUE (S). In other words, when transmission of a reference signal is requested from the BS, transmission of the error measurement request message from the BSmay be omitted.

1 1 2 1 1 10 FIG. A format of the error measurement request message transmitted by the BSmay be the format 3 shown in. The error measurement request field for the counterpart BS included in the error measurement request message of the BSmay indicate that the RUE does not transmit any request to the counterpart BS (e.g., BS). The error compensation BS request field included in the error measurement request message of the BSmay indicate that the BScompensates for a difference between transmission timing errors.

2 1 2 1 2 1106 1 1107 2 2 1109 The RUE may receive the reference signal from the BS, and may estimate a timing based on the received reference signal. After estimating the timings for the BSand BS, the RUE may calculate a difference between transmission timing errors of the BSand the transmission timing error of the BSbased on Equations 1 and 2 (S). The RUE may transmit an error measurement response message including the difference (e.g., difference value) between the transmission timing errors to the BS(S). When the error measurement request message of the BSis received, the RUE may transmit an error measurement response message including the difference between the transmission timing errors to the BS(S).

2 2 2 1 2 When the error measurement request message of the BSis not received (e.g., when only the reference signal of the BSis received), the RUE may not transmit the error measurement response message including the difference between transmission timing errors to the BS. In this case, the BSmay receive the error measurement response message from the RUE, and the BSmay not receive the error measurement response message from the RUE.

1 2 1108 1108 2 1 1103 1 2 1108 1 2 The BSmay transmit the difference between transmission timing errors to the BS(S). The step Smay be performed when the BSfails to receive an error measurement response message including the difference between transmission timing errors from the RUE. In other words, if the error measurement request message of the BSrequests transmission of the reference signal in the step S, the BSmay predict that BSdoes not receive the error measurement response message including the difference between transmission timing errors from the RUE. In this case, in the step S, the BSmay inform the BSof the difference between transmission timing errors.

The accuracy of absolute synchronization between the BSs may be improved based on the difference between transmission timing errors included in the error measurement response message. For example, when UEs belonging to the BSs perform a cooperative operation, each of the BSs may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

12 FIG. is a sequence chart illustrating a fifth exemplary embodiment of a method for avoiding transmission timing errors.

12 FIG. 1 2 1201 2 1 2 1 2 Referring to, a BSmay transmit an error measurement demand message to a BS(S). The error measurement demand message may include information indicating simultaneous or sequential transmission of reference signals. When simultaneous transmission of reference signals is difficult, sequential transmission of reference signals may be performed. The BSmay receive the error measurement demand message from the BS, and based on information included in the error measurement demand message, the BSmay identify that simultaneous transmission or sequential transmission of reference signals is requested. In addition, the error measurement demand message may include resource information of reference signals, and reference signal(s) of the BSand/or BSmay be transmitted in resources indicated by the error measurement demand message.

1 1 1202 1 2 1 2 1 The BSmay reserve resources (e.g., radio resources) for simultaneous or sequential transmission of reference signals. The BSmay transmit an error measurement request message including resource reservation information of reference signals to an RUE (S). The error measurement request message may include resource reservation information (e.g., transmission resource information) of reference signals of the BSand/or resource reservation information (e.g., transmission resource information) of reference signals of the BS. The RUE may receive the error measurement request message from the BSand may identify the resource reservation information of reference signals included in the error measurement request message. In addition, the BSmay identify the resource reservation information of reference signals by receiving the error measurement request message of the BS.

1 1203 2 1204 The BSmay transmit reference signals to the RUE in resources indicated by the error measurement demand message and/or the error measurement request message (S). The BSmay transmit reference signals to the RUE in resources indicated by the error measurement demand message and/or the error measurement request message (S). The reference signals may be transmitted based on a simultaneous transmission or sequential transmission scheme.

1 2 1 2 1 2 1205 1 1206 1 1 The RUE may receive the reference signals of the BSand the reference signals of the BSin the resources indicated by the error measurement message. The RUE may estimate timings based on the received reference signals. After estimating the timings for the BSand the BS, the RUE may calculate a difference between a transmission timing error of the BSand a transmission timing error of the BSbased on Equations 1 and 2 (S). The RUE may transmit an error measurement response message including the difference (e.g., difference value) between transmission timing errors to the BS(S). Since the error measurement request message is received from the BS, the RUE may transmit the error measurement response message to the BS.

1 1 2 1207 2 1 The BSmay receive the error measurement response message from the RUE, and may identify the difference between transmission timing errors included in the error measurement response message. The BSmay inform the BSof the difference between transmission timing errors (S). The BSmay receive the difference between transmission timing errors from the BS. The accuracy of absolute synchronization between the BSs may be improved based on the difference between transmission timing errors included in the error measurement response message. For example, when UEs belonging to the BSs perform a cooperative operation, each of the BSs may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

5 11 FIGS.to In the above-described exemplary embodiments (e.g., the exemplary embodiments of), the RUE may measure a difference of the transmission timing error with respect to the counterpart BS according to the request of the BS, and may report the difference of the transmission timing error to the BS. If there are many cooperating BSs and multiple RUEs, a procedure for the BS to identify which RUE among the RUEs registered to itself is connected to the cooperating BS (e.g., counterpart BS) may be required. The cooperating BS may be a BS desired to cooperate with.

The cooperating BSs may exchange lists of registered RUEs and may select one RUE among common RUEs based on the lists of registered RUEs. The list of registered RUEs may be referred to as an ‘RUE registration list’. The RUE registration list may include information on one or more RUEs registered to the BS (e.g., cooperating BS). The RUE may deliver a list of BSs (‘BS registration list’) to which the RUE is registered. In the transmission procedure of the error measurement request message, the BS(s) may select the counterpart BS in consideration of the BS registration list. The BS registration list may include information on one or more BSs to which the RUE is registered.

13 FIG. is a sequence chart illustrating a first exemplary embodiment of a method for exchanging BS registration lists.

13 FIG. 1 2 3 1301 1 2 3 1302 1 1 2 2 3 3 Referring to, a BS may request transmission of BS registration lists to RUEs (e.g., RUE, RUE, and RUE) registered therewith (S). The RUEs (e.g., RUE, RUE, and RUE) may receive the request for transmission of BS registrations list from the BS. In a step S, the RUEmay transmit a BS registration list including information of BS(s) to which the RUEis registered to the BS, the RUEmay transmit a BS registration list including information of BS(s) to which the RUEis registered to the BS, and the RUEmay transmit a BS registration list including information of BS(s) to which the RUEis registered to the BS. The BS may receive the BS registration lists from the RUEs. The BS may identify the RUE(s) registered in the cooperating BS(s) (e.g., counterpart BS(s)) based on the BS registration lists, and may transmit error measurement request message(s) to the identified RUE(s). In other words, a first BS may identify a common RUE registered in common with the first BS and a second BS based on the BS registration lists.

14 FIG. is a sequence chart illustrating a first exemplary embodiment of a method for exchanging RUE registration lists.

14 FIG. 2 3 4 1401 1 1402 2 1 3 1 4 1 Referring to, one or more RUEs may be registered with a BS. The BS may have an RUE registration list. The RUE registration list may include information on one or more RUEs registered to the BS. The BS may request transmission of RUE registration lists to neighboring BSs (e.g., BS, BS, and BS) (S). The neighboring BSs may receive the request for transmission of RUE registration lists from the BS. In a step S, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, and the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS.

1 1 1 1 1 2 1 2 1 2 3 4 The BSmay receive the RUE registration lists from the neighboring BSs. The BSmay identify RUEs registered with each BS based on the RUE registration lists. The BSmay identify a BS having a common RUE based on the RUE registration lists. For example, the BSmay determine that a common RUE registered with the BSand the BSexists. In this case, the BSmay perform a method of avoiding transmission timing errors with the BS. The BSs (e.g., BS, BS, BS, and BS) may be connected by wire. Since the exchange procedure of the RUE registration lists is performed over wires, radio resources are not wasted due to the exchange procedure of the RUE registration lists.

As another method proposed in the present disclosure, a primary BS may request error measurement to a common RUE among RUEs registered with neighboring BS(s). The primary BS may manage and/or control the cooperative BS(s) and may initiate the error measurement procedure. The neighboring BS(s) may be cooperating BS(s) for the primary BS. In other words, the neighboring BS(s) may be BS(s) the primary BS desires to cooperate with. The common RUE may mean an RUE registered with the BS(s).

15 FIG. is a conceptual diagram illustrating a first exemplary embodiment of a cooperation scenario between BSs.

15 FIG. 1 2 3 4 1 1 2 3 4 1 2 3 4 1 2 3 4 1 1 Referring to, a BSamong BSs may be a primary BS, and a BS, BS, and BSmay be cooperating BSs for the BS. The BS, BS, BS, and BSmay be connected to an RUE. In other words, the RUE may be registered with the BS, BS, BS, and BS. The RUE connected to (e.g., registered with) the BS, BS, BS, and BSmay be a common RUE. The BS(e.g., primary BS) may request transmission of reference signals from the BSs. The BSmay request simultaneous or sequential transmission of reference signals. The BSs may transmit reference signals. The RUE may measure the reference signal received from each of the BSs, and may calculate a difference between transmission timing errors of the BSs based on results of the measurement. The RUE may inform the BS(s) of the difference between transmission timing errors.

16 16 FIGS.A andB are sequence charts illustrating a first exemplary embodiment of a method for measuring and delivering differences between transmission timing errors.

16 16 FIGS.A andB 16 FIGS.A 15 FIG. 16 FIG.A 16 FIG.B 16 FIG.A 16 FIG.B 16 16 FIGS.A andB 16 FIG.A 16 FIG.B 16 1 2 3 4 1 1 2 3 4 1 2 3 4 1601 1 Referring to, the exemplary embodiments ofandB may be applied to the cooperation scenario shown in, the procedure ofmay be performed prior to the procedure of, and after completion of the procedure of, the procedure ofmay be performed. A BSmay be a primary BS, and a BS, BS, and BSmay be cooperating BSs for the BS. An RUE may be a common RUE for the BS, BS, BS, and BS. The procedures ofmay be respectively referred to as a configuration step (i.e.,) for measuring differences between transmission timing errors and a measurement/delivery step (i.e.,) of differences between transmission timing errors. In the configuration step for measuring differences between transmission timing errors, the BS(e.g., primary BS) may request transmission of RUE registrations list to cooperating BSs (e.g., BS, BS, and BS) (S). The cooperating BSs may be neighboring BSs or counterpart BSs of the BS.

1 1602 2 1 3 1 4 1 1 1 1 1 1 2 3 4 1 2 3 4 The cooperating BSs may receive the request for transmission of RUE registration lists from the BS. In a step S, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, and the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS. The BSmay receive RUE registration lists from the neighboring BSs. The BSmay identify an RUE registered in common with the cooperating BSs and may determine the BSas a common RUE based on the RUE registration lists. In other words, the BSmay identify a common RUE registered with the BS, BS, BS, and BS. The BS, BS, BS, and BSmay be connected to the common RUE.

1 1 1603 1 The BSmay negotiate with the cooperating BSs a time at which transmission of reference signals is possible, and based on a result of the negotiation, may reserve radio resources for transmission of reference signals. The BSmay transmit reference signal information (e.g., resource reservation information, transmission resource information) to each of the cooperating BSs (S). The reference signal information may include resource reservation information of reference signals for each of the cooperating BSs. The resource reservation information of reference signals may indicate radio resources reserved for transmission of reference signals and/or a transmission time of reference signals. The cooperating BSs may receive the reference signal information from the BSand, based on the received information, may identify the radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 1604 1603 1604 1 The BSmay transmit reference signal information (e.g., resource reservation information) to the RUE (e.g., common RUE) (S). The reference signal information transmitted in the step Smay be the same as the reference signal information transmitted in the step S. The RUE may receive the reference signal information from the BSand, based on the received information, may identify radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 2 3 4 1605 1606 1 2 1 3 1 4 In the measurement/delivery step of differences between transmission timing errors, each of the BS, BS, BS, and BSmay transmit reference signals to the RUE using reserved radio resources (S). The reference signals may be transmitted based on a simultaneous transmission scheme or a sequential transmission scheme. The reference signal may be DMRS, CSI-RS, PRS, and/or PT-RS. The RUE may receive the reference signals in reserved radio resources, and may calculate differences between transmission timing errors based on results of measurements of the reference signals (S). For example, the RUE may calculate the differences between transmission timing errors of the BSs based on Equation 1 and Equation 2. The RUE may calculate the difference between transmission timing errors of the BSand BS, the difference between transmission timing errors of the BSand BS, and the difference between transmission timing errors of the BSand BS.

1 1607 1 1 1608 The RUE may transmit information on the differences between transmission timing errors to the BS(S). The BSmay obtain information on the differences between transmission timing errors from the RUE. The BSmay transmit information on the differences between transmission timing errors to each of the cooperating BSs (S). The accuracy of absolute synchronization between BSs may be improved based on the differences between transmission timing errors. When BSs perform cooperative communication, the BSs may perform downlink transmission to the UE after compensating for differences between transmission timing errors. For example, each of the BSs may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

17 FIG. is a conceptual diagram illustrating a second exemplary embodiment of a cooperation scenario between BSs.

17 FIG. 1 2 3 4 5 1 1 2 3 4 1 1 1 2 3 4 1 5 2 2 1 5 1 1 2 1 1 2 1 2 Referring to, a BSamong BSs may be a primary BS, and BS, BS, BS, and BSmay be cooperating BSs for the BS. A common RUE for the BS, BS, BS, and BSmay be an RUE. In other words, the RUEmay be connected to the BS, BS, BS, and BS. A common RUE for the BSand BSmay be an RUE. In other words, the RUEmay be connected to the BSand BS. The BS(e.g., primary BS) may request transmission of reference signals from BSs connected to the RUEand/or RUE. The BSmay request simultaneous or sequential transmission of reference signals. The BSs may transmit reference signals. Each of the RUEand RUEmay measure the reference signals received from each of the BSs, and may calculate differences between transmission timing errors of the BSs based on results of the measurements. Each of the RUEand RUEmay inform the BS(s) of the differences between transmission timing errors.

18 18 FIGS.A andB are sequence charts illustrating a second exemplary embodiment of a method for measuring and delivering differences between transmission timing errors.

18 18 FIGS.A andB 18 18 FIGS.A andB 17 FIG. 17 FIG.A 17 FIG.B 18 FIG.A 18 FIG.B 18 18 FIGS.A andB 18 FIG.A 18 FIG.B 1 2 3 4 5 1 1 1 2 3 4 2 1 5 1 2 3 4 5 1801 1 Referring to, the exemplary embodiment ofmay be applied to the cooperation scenario shown in, the procedure ofmay be performed prior to the procedure of, and after completion of the procedure of, the procedure ofmay be performed. A BSmay be a primary BS, and a BS, BS, BS, and BSmay be cooperating BSs for the BS. An RUEmay be a common RUE for the BS, BS, BS, and BS, and an RUEmay be a common RUE for the BSand BS. The procedures ofmay be respectively referred to as a configuration step (i.e.,) for measuring differences between transmission timing errors and a measurement/delivery step (i.e.,) of differences between transmission timing errors. In the configuration step for measuring differences between transmission timing errors, the BS(e.g., primary BS) may request transmission of RUE registrations list to cooperating BSs (e.g., BS, BS, BS. BS) (S). The cooperating BSs may be neighboring BSs or counterpart BSs of the BS.

1 1802 2 1 3 1 4 1 5 1 1 1 1 1 1 1 2 3 4 1 2 1 5 The cooperating BSs may receive the request for transmission of RUE registration lists from the BS. In a step S, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, and the BSmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS. The BSmay receive RUE registration lists from the neighboring BSs. The BSmay identify an RUE registered in common with the cooperating BS. The BSmay identify a common RUE registered with the BSs. The BSmay determine the RUEas a common RUE for the BS, BS, BS, and BS, and the BSmay determine the RUEas a common RUE for the BSand BS.

1 1 2 3 4 1 1 5 2 1 1 The BSmay configure a first group including the BS, BS, BS, BS, and RUE, and may configure a second group including the BS, BS, and RUE. The BSmay negotiate with cooperating BSs belonging to the first group a time at which transmission of reference signals is possible, and reserve radio resources for transmission of reference signals based on a result of the negotiation. The BSmay negotiate with cooperating BSs belonging to the second group a time at which transmission of reference signals is possible, and reserve radio resources for transmission of reference signals based on a result of the negotiation.

1 1803 1 The BSmay transmit reference signal information (e.g., resource reservation information) to each of the cooperating BSs (S). The reference signal information may be classified into reference signal information for the first group and reference signal information for the second group. The reference signal information may include resource reservation information of reference signals for each of the cooperating BSs. The resource reservation information of reference signals may indicate radio resources reserved for transmission of reference signals and/or transmission time of reference signals. The cooperating BSs may receive the reference signal information from the BSand, based on the received information, may identify radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 1 1804 1 1 1 2 1805 2 1 The BSmay transmit reference signal information (e.g., resource reservation information) for the first group to the RUE(e.g., common RUE) (S). The RUEmay receive the reference signal information from the BS, and based on the received information, may identify the radio resources reserved for transmission of reference signals and/or transmission time of reference signals. The BSmay transmit reference signal information (e.g., resource reservation information) for the second group to the RUE(e.g., common RUE) (S). The RUEmay receive the reference signal information from the BS, and based on the received information, may identify the radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 2 3 4 1 1806 1 5 2 1807 1 1808 1 1 2 1 3 1 4 2 1809 2 1 5 1 2 In the step of measuring/delivering differences between transmission timing errors, each of the BS, BS, BS, and BSmay transmit reference signals to the RUEusing the reserved radio resource (S), and each of the BSand BSmay transmit reference signals to the RUEusing the reserved radio resources (S). The reference signals may be transmitted based on a simultaneous transmission scheme or a sequential transmission scheme. The reference signal may be a DMRS, CSI-RS, PRS, and/or PT-RS. The RUEmay receive reference signals in the reserved radio resources, and may calculate differences between transmission timing errors based on results of the measurements on the reference signals (S). The RUEmay calculate the difference between transmission timing errors of the BSand BS, the difference between transmission timing errors of the BSand BS, and the difference between transmission timing errors of the BSand BS. The RUEmay receive reference signals in the reserved radio resources, and may calculate a difference between transmission timing errors based on results of the measurements on the reference signals (S). The RUEmay calculate a difference between transmission timing errors of the BSand BS. Each of the RUEand RUEmay calculate the difference(s) between transmission timing errors of the BSs based on Equations 1 and 2.

1 1 1810 1 1 2 1 1811 1 2 1 1812 2 3 4 1 5 2 The RUEmay transmit information on the differences between transmission timing errors to the BS(S). The BSmay obtain the information on the differences between transmission timing errors from the RUE. The RUEmay transmit information on the differences between transmission timing errors to the BS(S). The BSmay obtain information on the differences between transmission timing errors from the RUE. The BSmay transmit information on the differences between transmission timing errors to each of the cooperating BSs (S). The differences between transmission timing errors transmitted to the BS, BS, and BSbelonging to the first group may be the differences between transmission timing errors calculated in the RUE. The differences between transmission timing errors transmitted to the BSbelonging to the second group may be the difference between transmission timing errors calculated in the RUE. The accuracy of absolute synchronization between the BSs may be improved based on the differences between transmission timing errors. When BSs perform cooperative communication, the BSs may perform downlink transmission to a UE after compensating for the differences between transmission timing errors. For example, each of the BSs may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

1 1 1 1 1 2 3 4 2 3 4 1 2 3 4 Table 1 below may show the differences between transmission timing errors measured in the RUE. The differences between transmission timing errors in Table 1 may be differences between transmission timing errors reported by the RUEto the BS. Table 1 may show differences between transmission timing errors measured based on the BS. Other BS(s) may perform transmission after compensating for the difference between transmission timing errors based on the BS. Alternatively, the differences between transmission timing errors based on the BS, BS, or BSmay be derived from Table 1. In this case, other BS(s) may perform transmission after compensating for the difference between transmission timing errors based on the BS, BS, or BS. The present disclosure includes a method for measuring/reporting the differences between transmission timing errors based on the BSas well as a method for measuring/reporting the differences between transmission timing errors based on other BSs (e.g., BS, BS, and BS).

TABLE 1 Counterpart Difference between transmission BS ID BS ID timing errors (ns) BS1 BS2 60 BS1 BS3 −50 BS1 BS4 +100

2 2 1 1 1 5 5 1 5 Table 2 below may show the differences between transmission timing errors measured in the RUE. The differences between transmission timing errors in Table 2 may be the differences between transmission timing errors reported by the RUEto the BS. Table 2 may show the differences between transmission timing errors measured based on the BS. Other BS(s) may perform transmission after compensating for the difference between transmission timing error based on the BS. Alternatively, the differences between transmission timing errors based on the BSmay be derived from Table 2. In this case, other BS(s) may perform transmission after compensating for the difference between transmission timing errors based on the BS. The present disclosure may include a method for measuring/reporting differences between transmission timing errors based on the BSas well as a method for measuring/reporting differences between transmission timing errors based on other BS (e.g., BS).

TABLE 2 Counterpart Difference between transmission BS ID BS ID timing errors (ns) BS1 BS5 30

17 FIG. 2 3 4 5 1 1 In the cooperation scenario shown in, cooperative communication between the BSs may be performed. In this case, each of the BS, BS, BS, and BSmay perform downlink transmission after compensating for the difference between transmission timing errors. Since downlink transmission is performed based on the BS, the BSmay perform downlink transmission without compensating for the difference between transmission timing errors. The downlink transmission may be a transmission operation of downlink data.

3 18 FIGS.to 19 25 FIGS.to According to the above-described exemplary embodiments (e.g., the exemplary embodiments of), the impact of transmission timing errors between different BSs may be eliminated. Alternatively, the impact of transmission timing errors between different BSs may be reduced. In order to achieve ATS in the wireless factory automation system, the following exemplary embodiments (e.g., exemplary embodiments of) may be considered.

3 18 FIGS.to In the exemplary embodiments of, even when a first UE (e.g., arbitrary UE) is not an RUE, if the first UE accurately know propagation delays (or distances) between the first UE and BS(s), the first UE may perform a role of an RUE.

In order to achieve ATS between UEs belonging to a single BS in the wireless factory automation system, a method of removing influences of transmission timing errors using an RUE may be used.

19 FIG. is a conceptual diagram illustrating a sixth exemplary embodiment of transmission timing errors.

19 FIG. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 BS1,UE1 BS1,UE1,TX BS1,UE1,RX Referring to, a BSand a TRPmay exist, the BSmay be a single BS, the TRPmay be a single TRP, and the TRPmay belong to the BS. The BSmay be connected with a plurality of UEs. In other words, the plurality of UEs may exist within a coverage of the BS. When the BStransmits a signal to a UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the BSand a reception timing error eoccurring at the UEmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BSand/or UEcannot know the transmission timing error. In addition, the BSand/or UEcannot control the transmission timing error.

1 1 2 1 2 1 1 2 1 1 2 TRP1,UE2 TRP1,UE2,TX TRP1,UE2,RX When the TRPbelonging to the BStransmits a signal to a UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the TRPand a reception timing error eoccurring at the UEmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the BS, TRP, and/or UEcannot know the transmission timing error. In addition, the BS, TRP, and/or UEcannot control the transmission timing error.

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 BS1,RUE1 TRP1,RUE1 If an RUEis located between the BSand TRP(e.g. TRPbelonging to the BS), transmission timing errors caused by the BSand TRPcannot be identified, but a difference between the transmission timing errors of the BSand TRPmay be identified using the RUE. The BSand TRPmay know the location of the RUE. The location of the RUEmay be a location having good radio fading channel qualities for the BSand the TRP, a location where there is no change in the radio fading channel qualities, or a location where a change in the radio fading channel qualities is insignificant. The BSand/or RUEmay know the propagation delay τfrom the BSto the RUE, and the TRPand/or RUEmay know the propagation delay τfrom the TRPto the RUE.

BS1,RUE1,RX TRP1,RUE1,RX 1 1 1 1 1 1 1 1 1 The reception timing errors eand efor the BS, TRP, and RUEmay be almost the same when the radio link quality of each of the BSand TRPis above a predefined criterion. In the present disclosure, the BSand TRPmay be assumed to be connected by wire, and synchronization between the BSand TRPmay be assumed to be very accurate absolute synchronization.

1 1 1 1 1 1 1 1 1 1 BS1,RUE1 TRP1,RUE1 BS1,RUE1 TRP1,RUE1 BS1,RUE1 TRP1,RUE1 The BSand TRPmay transmit signals for absolute synchronization simultaneously or at predefined timings (e.g., sample time points). The signals for absolute synchronization may be referred to as absolute synchronization signals. The absolute synchronization signals may be transmitted periodically or aperiodically. Based on Equation 3 below, the RUEmay measure a difference between an arrival time Tof the signal (e.g., absolute synchronization signal) transmitted from the BSand an arrival time Tof the signal (e.g., absolute synchronization signal) transmitted from the TRPbased on Equation 3 below. In other words, the RUEmay measure T−T. Tmay mean a time when the absolute synchronization signal transmitted by the BSarrives at the RUE. Tmay mean a time when the absolute synchronization signal transmitted by the TRParrives at the RUE.

BS1,RUE1 TRP1,RUE1 1 When the difference τ−τbetween the propagation delays is denoted as A in Equation 3, the RUEmay measure or estimate a difference B between transmission timing errors based on a difference between the arrival times and A. B may be defined as in Equation 4 below.

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 The RUEmay transmit (e.g., signal) B or information related to B to the BSand/or TRP. The BSand/or TRPmay receive B or the information related to B from the RUE. The BSand/or TRPmay transmit B or the information related to B to a control station (e.g., controller) that manages and/or controls the BS(s). The control station may receive B or the information related to B from the BSand/or TRP. The control station may adjust the transmission time(s) (e.g., sample time point(s)) of the BSand/or TRPusing B or the information related to B. Alternatively, the RUEmay transmit (e.g., signal) information on the transmission times (e.g., sample time points) of the BSand/or TRPto the BSand/or TRPwithout a control station.

1 2 According to the above-described operation, as shown in Equation 5 below, transmission timing errors for the UEand UEbelonging to a single BS may not be eliminated, but the transmission timing errors may be adjusted to be equal.

1 1 2 According to Equation 5, the TRPmay adjust the transmission timing by adding the difference B between transmission timing errors to the existing transmission timing. According to the above-described operation, the UEand UEmay achieve ATS without impact of the transmission timing errors. Accordingly, sophisticated cooperative operations may be performed.

1 1 1 1 1 When the control station that manages and/or controls BS, the RUE, or the BStransmits information requesting adjustment of the transmission time, the information may include the difference B between transmission timing errors in Equation 5 and/or an indication of a scheme of adjusting the transmission timing errors to be equal. The method of adjusting the transmission timing errors to be equal may be a scheme of advancing the transmission time of the BSby B/2 or a scheme of delaying the transmission time of the TRPby B/2.

20 FIG. is a conceptual diagram illustrating a first exemplary embodiment of a cooperation scenario of a BS and TRPs.

20 FIG. 1 2 1 2 1 3 2 1 2 1 2 1 1 2 3 1 2 1 2 3 Referring to, a BS may be connected to a TRPand TRPby wires. A UEmay be registered with the BS, a UEmay be registered with the TRP, and a UEmay be registered with the TRP. An RUE may be registered with all of the BS, TRP, and TRP. The BS may serve as a digital unit (DU) for the TRPand TRP. For example, the BS may perform a function of digital signal processing. In addition, the BS may communicate with the UEthrough a radio access link. Absolute synchronization should be established between the UE, UE, and UEfor cooperative communication. Each of the BS, TRP, and TRPmay obtain a difference between transmission timing errors, and may perform communication after compensating for the difference between transmission timing errors. According to the above-described operation, absolute synchronization between the UE, UE, and UEmay be achieved.

21 21 FIGS.A andB are sequence charts illustrating a third exemplary embodiment of a method for measuring and delivering differences between transmission timing errors.

21 21 FIGS.A andB 21 21 FIGS.A andB 20 FIG. 21 FIG.A 21 FIG.B 21 FIG.B 21 FIG.A 21 21 FIGS.A andB 21 FIG.A 21 FIG.B 1 2 2101 Referring to, the exemplary embodiment ofmay be applied to the cooperation scenario shown in, the procedure ofmay be performed prior to the procedure of, and the procedure ofmay be performed after completion of the procedure of. The procedures ofmay be respectively referred to as a configuration step for measuring differences between transmission timing errors (e.g., the procedure of) and a measurement/delivery step of differences between transmission timing errors (e.g.,). In the configuration step for measuring differences between transmission timing errors, the BS may request the TRPs (e.g., TRPand TRP) to transmit RUE registration lists (S). The BS may request transmission of the RUE registration lists to the TRPs with which the UE(s), which are cooperative communication targets, are registered.

2102 1 2 1 2 1 2 The TRPs may receive the request for transmission of RUE registration lists from the BS. In a step S, the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, and the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS. The BS may receive the RUE registration lists from the TRPs. The BS may identify an RUE commonly registered with the TRPs and may identify an RUE commonly registered with the TRPs based on the RUE registration lists. In other words, the BS may identify a common RUE registered with the BS, TRP, and TRP. The BS, TRP, and TRPmay be connected to the common RUE.

2103 The BS may negotiate with the TRPs a time at which transmission of references signal is possible, and may reserve radio resources for transmission of reference signals based on a result of the negotiation. The BS may transmit reference signal information (e.g., resource reservation information, transmission resource information) to each of the TRPs (S). The reference signal information may include resource reservation information of reference signals for each of the TRPs. The resource reservation information of reference signals may indicate radio resources reserved for transmission of reference signals and/or a transmission time of reference signals. The TRPs may receive the reference signal information from the BS, and may identify radio resources reserved for transmission of reference signals and/or the transmission time of reference signals based on the received information.

2104 2103 2104 The BS may transmit reference signal information (e.g., resource reservation information) to the RUE (e.g., common RUE) (S). The reference signal information transmitted in the step Smay be the same as the reference signal information transmitted in the step S. The RUE may receive the reference signal information from the BS, and based on the received information, may identify radio resources reserved for transmission of reference signals and/or the transmission time of reference signals.

1 2 2105 2106 1 2 In the step of measuring/delivering differences between transmission timing errors, each of the BS, TRP, and TRPmay transmit reference signals to the RUE using reserved radio resources (S). The reference signals may be transmitted based on a simultaneous transmission scheme or a sequential transmission scheme. The reference signal may be DMRS, CSI-RS, PRS, and/or PT-RS. The RUE may receive the reference signals in the reserved radio resources, and may calculate differences between transmission timing errors based on results of the measurements on the reference signals (S). For example, the RUE may calculate differences between transmission timing errors of communication nodes based on Equations 3 and 4 (or Equations 1 and 2). The RUE may calculate a difference between transmission timing errors of the BS and TRPand a difference between transmission timing errors of the BS and TRP.

2107 2108 The RUE may transmit information on the differences between transmission timing errors to the BS (S). The BS may obtain the information of the differences between transmission timing errors from the RUE. The BS may transmit information on the difference between transmission timing errors to each of the TRPs (S). Accuracy of absolute synchronization between the communication nodes (e.g., BS, TRP) may be improved based on the differences between transmission timing errors. When the BS and the TRPs perform cooperative communication, each of the BS and the TRPs may perform downlink transmission to the UE after compensating for the difference between transmission timing errors. For example, each of the communication nodes may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

22 22 FIGS.A andB are sequence charts illustrating a fourth exemplary embodiment of a method for measuring and delivering differences between transmission timing errors.

22 22 FIGS.A andB 22 22 FIGS.A andB 20 FIG. 22 FIG.A 22 FIG.B 22 FIG.B 22 FIG.A 22 22 FIGS.A andB 22 FIG.A 22 FIG.B 2201 Referring to, the exemplary embodiment ofmay be applied to the cooperation scenario shown in, the procedure ofmay be performed prior to the procedure of, and the procedure ofmay be performed after completion of the procedure of. The procedures ofmay be respectively referred to as a configuration step for measuring differences between transmission timing errors (e.g., the procedure of) and a measurement/delivery step of differences between transmission timing errors (e.g.,). In the configuration step for measuring differences between transmission timing errors, the BS may request transmission of a TRP registration list from an RUE (S). The BS may request information of TRP(s) with which the RUE is registered.

2202 1 2 1 2 The RUE may receive the request for transmission of a TRP registration list from the BS. The RUE may transmit a TRP registration list including information of TRP(s) with which the RUE is registered to the BS (S). The BS may receive the TRP registration list from the RUE. The BS may select TRP(s) to which UE(s), which are cooperative communication targets, are connected among TRPs indicated by the TRP registration list. For example, the BS may select a TRPand TRP. The UE(s) that are the target(s) of cooperative communication may belong to the TRPand TRP.

2203 The BS may negotiate with the TRPs a time at which transmission of reference signals is possible, and may reserve radio resources for transmission of reference signals based on a result of the negotiation. The BS may transmit reference signal information (e.g., resource reservation information, transmission resource information) to each of the TRPs (S). The reference signal information may include resource reservation information of reference signals for each of the TRPs. The resource reservation information of reference signals may indicate radio resources reserved for transmission of reference signals and/or a transmission time of reference signals. The TRPs may receive the reference signal information from the BS, and may identify radio resources reserved for transmission of reference signals and/or the transmission time of reference signals based on the received information.

2204 2203 2204 The BS may transmit reference signal information (e.g., resource reservation information) to the RUE (e.g., common RUE) (S). The reference signal information transmitted in the step Smay be the same as the reference signal information transmitted in the step S. The RUE may receive the reference signal information from the BS, and based on the received information, may identify radio resources reserved for transmission of reference signals and/or the transmission time of reference signals.

1 2 2205 2206 1 2 In the measurement/delivery step of differences between transmission timing errors, each of the BS, TRP, and TRPmay transmit reference signals to the RUE using reserved radio resources (S). The reference signals may be transmitted based on a simultaneous transmission scheme or a sequential transmission scheme. The reference signal may be a DMRS, CSI-RS, PRS, and/or PT-RS. The RUE may receive reference signals in reserved radio resources, and calculate differences between transmission timing errors based on results of measurements on the reference signals (S). For example, the RUE may calculate differences between transmission timing errors of communication nodes based on Equations 3 and 4 (or Equations 1 and 2). The RUE may calculate a difference between transmission timing errors between the BS and TRPand a difference between transmission timing errors between the BS and TRP.

2207 2208 The RUE may transmit information on the differences between transmission timing errors to the BS (S). The BS may obtain the information on the differences between transmission timing errors from the RUE. The BS may transmit information on the differences between transmission timing errors to each of the TRPs (S). Accuracy of absolute synchronization between the communication nodes (e.g., BS, TRP) may be improved based on the difference between transmission timing errors. When the BS and the TRP perform cooperative communication, each of the BS and the TRP may perform downlink transmission to the UE after compensating for the difference between transmission timing errors. For example, each of the communication nodes may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

1 2 1 2 1 2 Table 3 below may show differences between transmission timing errors measured in the RUE. The differences between transmission timing errors in Table 3 may be the differences between transmission timing errors reported by the RUE to the BS. The BS may share the differences between transmission timing errors with the TRPand TRP. When the BS, TRP, and TRPperform cooperative communication, each of the TRPand TRPmay perform downlink transmission after compensating for the difference between transmission timing errors in Table 3. Since downlink transmission is performed based on the BS, the BS may perform downlink transmission without compensating for a difference between transmission timing errors. The downlink transmission may be a transmission operation of downlink data.

TABLE 3 Counterpart Difference between transmission BS ID TRP ID timing errors (ns) BS1 TRP1 60 BS1 TRP2 −50

23 FIG. is a sequence chart illustrating a seventh exemplary embodiment of a method for avoiding transmission timing errors.

23 FIG. 1 2 1 2 1 2 1 1 1 1 1 1 1 1 TRP1,UE1 TRP1,UE1,TX TRP1,UE1,RX Referring to, a single BS may exist, and a plurality of TRPs (e.g., TRPand TRP) may belong to the BS. The BS may be connected with a plurality of UEs. Each of the TRPand TRPmay be connected to a plurality of UEs. In other words, a plurality of UEs may exist within a coverage of each the TRPand TRP. When the TRPtransmits a signal to a UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the TRPand a reception timing error eat the UEmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the TRPand/or UEcannot know the transmission timing error. In addition, the TRPand/or UEcannot control the transmission timing error.

2 2 2 2 2 2 1 2 2 TRP2,UE2 TRP2,UE2,TX TRP2,UE2,RX When the TRPtransmits a signal to a UE, in addition to a radio propagation delay τ, a transmission timing error eoccurring at the TRPand a reception timing error eoccurring at the UEmay exist. The reception timing error may be overcome to some extent through a sophisticated design of a physical layer numerology. Since the transmission timing error is due to a hardware impairment inherent in a communication node, the TRPand/or UEcannot know the transmission timing error. In addition, the BS, TRPand/or UEcannot control the transmission timing error.

24 FIG. is a conceptual diagram illustrating a first exemplary embodiment of a cooperation scenario of TRPs.

24 FIG. 24 FIG. 1 2 3 4 1 2 3 1 3 4 2 Referring to, a plurality of TRPs (e.g., TRP, TRP, TRP, and TRP) may be connected to one BS by wires. The TRP, TRP, and TRPmay be connected to a common RUE, RUE. The TRPand TRPmay be connected to a common RUE, RUE. In the cooperation scenario of, a method for measuring/reporting differences between transmission timing errors of TRPs may be required for cooperative communication. Each of the TRPs may be connected to the BS by wire. Each of the TRPs may receive reference signal information for measuring differences between transmission timing errors from the BS. In other words, the BS may request each of the TRP to transmit reference signals.

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 1 3 4 2 The BS may obtain differences between transmission timing errors for the TRP, TRP, TRP, and TRPto perform cooperative communication among the TRPs connected to the BS. The BS may deliver the differences between transmission timing errors to the TRP, TRP, TRP, and TRP. Each of the TRP, TRP, TRP, and TRPmay perform transmission after compensating for the differences between transmission timing errors. The TRP, TRP, and TRPmay be connected to the RUE, and the TRPand TRPmay be connected to the RUE.

25 25 FIGS.A andB are sequence charts illustrating a fifth exemplary embodiment of a method for measuring and delivering differences between transmission timing errors.

25 25 FIGS.A andB 25 25 FIGS.A andB 24 FIG. 25 FIG.A 25 FIG.B 25 FIG.B 25 FIG.A 25 25 FIGS.A andB 25 FIG.A 25 FIG.B 1 2 3 4 1 2 3 4 2501 Referring to, the exemplary embodiment ofmay be applied to the cooperation scenario shown in, the procedure ofmay be performed prior to the procedure of, and the procedure ofmay be performed after completion of the procedure of. The BS may be connected to the TRP, TRP, TRP, and TRP. The procedures ofmay be respectively referred to as a configuration step for measuring differences between transmission timing errors (e.g., procedure of) and a measurement/delivery step of differences between transmission timing errors (e.g., procedure of). In the configuration step for measuring differences between transmission timing errors, the BS may request the TRPs (e.g., TRP, TRP, TRP, and TRP), which are to perform cooperative communication, to transmit RUE registrations lists (S).

2502 1 2 3 4 1 1 2 3 2 3 4 The TRPs may receive the request for transmission of RUE registration lists from the BS. In a step S, the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS, and the TRPmay transmit an RUE registration list including information of RUE(s) registered therewith to the BS. The BS may receive RUE registration lists from the TRPs. The BS may identify an RUE commonly registered with the TRPs based on the RUE registration lists. The BS may determine an RUEas a common RUE for the TRP, TRP, and TRP. The BS may determine an RUEas a common RUE for the TRPand TRP.

1 2 3 1 1 3 4 2 4 1 4 The BS may configure a first group including the TRP, TRP, TRP, and RUE. The BS may designate the TRPas a primary TRP of the first group. The BS may configure a second group including the TRP, TRP, and RUE. The BS may designate the TRPas a primary TRP of the second group. The primary TRP may perform a radio resource reservation function, a function for receiving information on differences between transmission timing errors, and/or a function of delivering information on differences between transmission timing errors. The TRP(e.g., primary TRP) may negotiate with cooperative TRPs belonging to the first group a time at which transmission of reference signals is possible, and reserve radio resources for transmission of reference signals based on a result of the negotiation. The TRP(e.g., primary TRP) may negotiate with cooperative TRPs belonging to the second group a time at which transmission of reference signals is possible, and reserve radio resources for transmission of reference signals based on a result of the negotiation.

1 2 3 2503 4 3 2504 2 3 1 3 4 The TRPmay transmit reference signal information (e.g., resource reservation information) to each of the TRPand TRPbelonging to the first group (S). The TRPmay transmit reference signal information (e.g., resource reservation information, transmission resource information) to the TRPbelonging to the second group (S). The reference signal information may include resource reservation information of reference signals for each of the TRPs. The resource reservation information of reference signals may indicate radio resources reserved for transmission of reference signals and/or the transmission time of reference signals. Each of the TRPand TRPmay receive reference signal information for the first group from the TRP, and based on the received information, may determine radio resources reserved for transmission of reference signals and/or transmission time of reference signals. The TRPmay receive the reference signal information for the second group from the TRP, and based on the received information, may identify radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 1 2505 1 1 4 2 2506 2 4 The TRPmay transmit reference signal information (e.g., resource reservation information, transmission resource information) for the first group to the RUE(e.g., common RUE) (S). The RUEmay receive the reference signal information from the TRP, and based on the received information, may identify radio resources reserved for transmission of reference signals and/or transmission time of reference signals. The TRPmay transmit reference signal information (e.g., resource reservation information, transmission resource information) for the second group to the RUE(e.g., common RUE) (S). The RUEmay receive the reference signal information from the TRP, and based on the received information, may identify radio resources reserved for transmission of reference signals and/or transmission time of reference signals.

1 2 3 1 2507 3 4 2 2508 1 2509 1 1 2 1 3 2 2510 2 4 3 1 2 In the measurement/delivery step of differences between transmission timing errors, each of the TRP, TRP, and TRPmay transmit reference signals to the RUEusing reserved radio resources (S), and each of the TRPand TRPmay transmit reference signals to the RUEusing reserved radio resources (S). The reference signals may be transmitted based on a simultaneous transmission scheme or a sequential transmission scheme. The reference signal may be a DMRS, CSI-RS, PRS, and/or PT-RS. The RUEmay receive the reference signals in the reserved radio resources, and may calculate differences between transmission timing errors based on results of measurements on the reference signals (S). The RUEmay calculate the difference between transmission timing errors of the TRPand TRPand the difference between transmission timing errors of the TRPand TRP. The RUEmay receive the reference signals in the reserved radio resources, and may calculate differences between transmission timing errors based on results of measurements on the reference signals (S). The RUEmay calculate the difference between transmission timing errors of the TRPand TRP. Each of the RUEand RUEmay calculate the difference between transmission timing errors of the BSs based on Equations 1 and 2.

1 1 2511 1 1 1 2512 1 2 4 2513 4 2 4 2514 4 The RUEmay transmit information on the difference between transmission timing errors to the TRP(e.g., primary TRP) (S). The TRPmay obtain information on the difference between transmission timing errors from the RUE. The TPRmay transmit information on the difference between transmission timing errors to the BS (S). The BS may obtain information on the difference between transmission timing errors from the TRP. The RUEmay transmit information on the difference between transmission timing errors to the TRP(e.g., primary TRP) (S). The TRPmay obtain information on the difference between transmission timing errors from the RUE. The TPRmay transmit information on the difference between transmission timing errors to the BS (S). The BS may obtain the information on the difference between transmission timing errors from the TRP.

1 2 3 4 1 4 4 1 1 2 3 4 2515 1 The BS may generate differences between transmission timing errors for all TRPs (e.g., TRP, TRP, TRP, and TRP) performing cooperative communication based on the difference in transmission timing error of TRPand transmission timing error of TRP. In other words, the BS may compensate for the difference in transmission timing error of TRPbased on TRP, and may generate differences between transmission timing errors for all TRPs (e.g., TRP, TRP, TRP, and TRP) performing cooperative communication in consideration of the compensated difference between transmission timing errors. The BS may transmit the difference in transmission timing error to each of the TRPs (S). Each of the TRPs may obtain the difference in transmission timing error from the BS. The accuracy of absolute synchronization between the TPRs may be improved based on the differences between transmission timing errors. In cooperative communication, each of the TRPs may perform downlink transmission after compensating for the differences between transmission timing errors based on the TRP. For example, each of the TRPs may transmit a signal earlier or later by the difference between transmission timing errors in order to improve accuracy of absolute synchronization.

1 1 1 1 Table 4 below may show differences between transmission timing errors measured in the RUE. The differences between transmission timing errors in Table 4 may be the differences between transmission timing errors reported by the RUEto the TRP. Table 4 may represent differences between transmission timing errors measured based on the TRP.

TABLE 4 Counterpart Difference between transmission TRP ID TRP ID timing errors (ns) TRP1 TRP2 −20 TRP1 TRP3 50

2 2 4 4 Table 5 below may show differences between transmission timing errors measured in the RUE. The differences between transmission timing errors in Table 5 may be the differences between transmission timing errors reported by the RUEto the TRP. Table 5 may show differences between transmission timing errors measured based on the TRP.

TABLE 5 Counterpart Difference between transmission TRP ID TRP ID timing errors (ns) TRP4 TRP3 30

1 1 2 3 4 1 4 1 2 1 4 The BS may compensate for the differences between transmission timing errors of Table 5 based on the TRP, and may generate differences between transmission timing errors for all TRPs (e.g., TRP, TRP, TRP, TRP) performing cooperative communication in consideration of the compensated difference between transmission timing errors. Table 6 may show differences between transmission timing errors for all TRPs performing cooperative communication. The BS may derive the difference between transmission timing errors of the TRPand TRPbased on the difference between transmission timing error measured at the RUEand the difference between transmission timing errors measured at the RUE. The TRPmay not be directly connected to the TRP.

TABLE 6 Counterpart Difference between transmission TRP ID TRP ID timing errors (ns) TRP1 TRP2 −20 TRP1 TRP3 50 TRP1 TRP4 20

19 25 FIGS.to In the above-described exemplary embodiments (e.g., the exemplary embodiments of), even when a first UE (e.g., arbitrary UE) is not an RUE, if the first UE accurately knows propagation delay(s) (or distance(s)) between the first UE and BS(s), the first UE may perform a role of an RUE.

The operations of the method according to the exemplary embodiment of the present disclosure can be implemented as a computer readable program or code in a computer readable recording medium. The computer readable recording medium may include all kinds of recording apparatus for storing data which can be read by a computer system. Furthermore, the computer readable recording medium may store and execute programs or codes which can be distributed in computer systems connected through a network and read through computers in a distributed manner.

The computer readable recording medium may include a hardware apparatus which is specifically configured to store and execute a program command, such as a ROM, RAM or flash memory. The program command may include not only machine language codes created by a compiler, but also high-level language codes which can be executed by a computer using an interpreter. The hardware device described above may be configured to operate with at least one software module to perform the operations of the present disclosure, and vice versa.

Although the present disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.